Electrodeposition of copper



2,873,234 ELECTRODEPOSITION OF COPPER Frank Passal, Detroit, Mich., assignor to Metal & Thermit Corporation, Woodbridge Township, N. J., a corporation of ew Jersey No Drawing. Application June 19, 1957 Serail No. 666,766

9 Claims. (Cl. 204-52) This invention relates to electroplating of copper and more particularly to the electrodeposition of bright copper plates.

Electrodeposited copper is widely used as a decorative finish and also as an undercoat for subsequent electrodeposits such as nickel baths acceptacle to industry are desirably economic, stable, easy to maintain, and should have good plating characteristics. Alkaline-cyanide type baths are widely used because of their relatively high plating speeds, excellent throwing power, and ease of maintenance. Alkaline-cyanide electroplating baths, and processes are described in Modern Electroplating, edited by A. G. Gray, pages 194-225 (1953).

I have now discovered a process for plating bright electrolytic copper from alkaline-cyanide baths containing novel additives.

It is an object of this invention to provide an efficient and economical process for electrodepositing bright and smooth copper deposits.

Another object of the invention is to provide bath compositions of the alkaline-cyanide type from which bright copper plate is electrodeposited.

Still another object of the invention is to provide compositions of matter which, when dissolved in water, yield alkaline-cyanide electrolytes suitable for the electrodeposition of bright copper electrodeposits.

Generally speaking, the invention contemplates-elem trodepositing copper from an alkaline-cyanide copper plating bath containing a small but effective amount of a compound having the general formula (herein referred to as a selenium bisdithiocarbamate), wherein R and R may be the same or different and are selected from the class consisting of hydrogen and alkyl hydrocarbon groups having up to 6 carbon atoms in the group. R and R within the scope of the invention include hydrogen and alkyl groups such as methyl, ethyl, propyl, butyl, amyl and hexyl, and the branched as well as the straight chain groups. The R and R groups may be replaced with a single alkyl cyclic compound, which may be viewed as a joinder of the R and R groups and include compounds having a total of to 7 carbon atoms in the ring. Selenium bisdiethyldithiocarbamate is the preferred additive.

Between about 0.001 g./l. (grams per liter) and 0.01 g./l., and preferably between about 0.002 g./l. and about 0.006 g./l. of the selenium bisdithiocarbamate is included in the alkaline-cyanide copper plating baths.

and/ or chromium. Electroplatingt 2 Conventional alkaline-cyanide baths and process conditions for electrodeposition are utilized in the present invention. Typical baths and process are illustrated in the table below: a

Range CuCN g./l 30-90 KCN g./l.. 49-145 K CO g./l 0-112 KOH g./l 7.5-37.5 KCN (free-adjust ed to and maintained) g'./l.. 5.6-1l.2 pH 1343.3 Temp F 130-180 Cathode c. D a. s. rm 10-50 10-50 Anode C. D a. s. f

The above table specifies baths and process limitations commercially preferred, and it is understood thatthe compositions and conditions may be varied somewhat,

and that in certain cases it may be desirable to vary these limitations. The potassium salts noted in the table, which are preferred, may be partially or completely replaced by sodium salts.

The copper electrodeposits obtained from baths utilizing selenium bisdithiocarbamate additions are substantially mirror bright. The electrodeposits prepared from the selenium bisdithiocarbamate-containing baths may be obtained in an even brighter condition by utilizing auxiliary or cooperating brightening additives in conjunction with the primary selenium bisdithiocarbamate. Such auxiliary additives include relatively small amounts of salts of lead, bismuth, antimony, or zinc, e. g., lead acetate, bismuth citrate, potassium antimony tartrate, zinc chloride, zinc sulfate, etc.

The alkaline-cyanide baths utilized should preferably contain a compound selected from the class consisting of the alkali metal tartrates, citrates, gluconates, and saccharates to improve current efiiciencies. I

Conventional wetting agents of the kind generally used in alkaline-cyanide copper electroplating baths are preferably incorporated in the baths. These include quaternary amine wetting agents such as C-decylbetaine and the ammonium hydroxide derivatives such as trimethylbenzylammonium chloride. We prefer novel and stable wetting agents of the following general structure: RNHCH -CH -COONa (an alkyl ,B-amino propionate), orRN(CH CH COONa) (an alkyl ,B-amino dipropiohate). The above compounds, marketed under the trade name Deriphats, are used-in concentrations of 0.01 to 0.1 gram per liter. They are stable in the electrolyte and even impart some brightening action. A compound of this class which has been successfully used is the sodium salt of a coconut alcohol derivative of fl-amino propionate, designated as Deriphat 151.

Best results are usually achieved when utilizing in the electrodeposition process a method of preventing the thin film immediately ad acent to the cathode from benot limited thereto.

Example N0. 1

CuCN 45 g./l. KCN 72.5 g./l. KOH 15 g./l. KC H O 45 g./l. (potassium gluconate). Selenium diethyl dithiocarbamate 0.004 g./1. Deriphat 151 0.05 g./l.

' Example N0. 2

CuCN. 45 g./l. KCN 72.5 g./l. KOH 15 g./l. K C H O 45 g./l. (potassium saccharate). Selenium diethyl dithiocarbamate 0.004 g./l. Pb(C l-I O 3H O 0.0037 g./l. (.002 g./l. Pb). Deriphat151 0.05 g./l.

. Example No.3

CuCN 67 g./l. KCN 110 g./l. KOH -l 30 g./l. KNaC H O -4H O 45 g./l. (Rochelle salt). Selenium dibutyl dithiocarbamate 0.004 g./l.

' Pb(C H O -3H O 0.0037 g./1. (.002 g./l. Pb).

Deriphat 151 0.05 g./l.

The bright copper electrodeposits obtained from the selenium bisdithiocarbamate containing alkaline-cyanide baths of the present invention are obtained on such conventional basis metals as iron, steel, nickel, zinc, lead, copper, etc., and alloys thereof. On certain basis metals such as iron or steel and zinc-base die-castings the basis metal is first given an initial thin flash of copper from a low eificiency cyanide copper bath.

It has been possible by various prior art processes to obtain semi-bright or mirror bright deposits by using various lead, zinc, or selenium additives. The following United States Patents and applications disclose such semi-bright or bright plating from baths containing selenium additions: Pat. Nos. 2,770,587; 2,737,485; 2,732,336; 2,701,234; 2,694,677; A. P. C. Serial No. 351,241-May 18, 1943. The only selenium compounds previously thought to function as brighteners were water soluble selenium compounds in which the selenium is ionically bound to the other atoms in the compound. In all of the prior compounds used, the selenium acts as a non-metal, the compounds being analogues of sulphur and/or oxygen-containing compounds, i. e., the selenium atoms were essentially non-metallic in nature. The results achieved by utilizing the selenium bisdithiocarbamates, which are virtually water insoluble and wherein the selenium acts as a metal and is bonded by covalent bonds, as far superior to those achieved when utilizing the compounds disclosed in the art as additives.

As many embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention includes all such modifications and variations as come within the scope of the appended claims.

I claim:

1. An alkyline-cyanide bath for bright copper plating comprising copper cyanide and, as a brightening agent more than 0.001 g./1. of at least one selenium bisdithiocarbarnate having the general formula:

'contains at least one secondary brightening agent selected from the class consisting of the salts of lead, bismuth, antimony and zinc.

6. In the process of electrodepositing copper from an alkaline-cyanide copper bath comprising copper cyanide, the improvement which comprises incorporating in said bath more than 0.001 g./l. of a selenium bisdithiocarbamate having the general formula:

wherein R and. R are selected from the class consisting of hydrogen alkyl groups having up to six carbon atoms.

7. The process as claimed in claim 6 in which between about 0.002 g./l. and 0.006 g./l. of selenium diethyldithiocarbamate is incorporated in the bath.

8. A bath solution according to claim 1 which also contains an alkali metal gluconate.

9. A bath solution according to claim 1 which also contains an alkali metal saccharate.

References Sited in the file of this patent UNITED STATES PATENTS 2,732,336 Ostrow Ian. 24, 1956 2,737,485 Overcash et a1. Mar. 6, 1956 2,770,587 Ostrow Nov. 13, 1956 2,773,022 Turner Dec. 4, 1956 

1. AN ALKYLINE-CYANIDE BATH FOR BRIGHT COPPER PLATING COMPRISING COPPER CYANIDE AND, AS A BRIGHTENING AGENT MORE THAN 0.001 G.$ OF A LEAST ONE SELENIUM BISDITHIOCARBAMATE HAVING THE GENERAL FORMULA: 